The present invention relates to an intake air system for a rotary engine and, more particularly, to a plenum chamber and tuned intake air conduit which receives cooling air from the engine and directs it to the carburetor for mixture and intake with the fuel.
The rotary internal combustion engine has gained significant acceptance and is being used more widely in a variety of automotive applications. One of the major attractions of the rotary engine is its relative simplicity of construction as compared to more conventional reciprocating piston engines. In addition, advances in engineering technology have eliminated or substantially alleviated certain design and operational problems previously associated with rotary piston engines, such as rotor seal efficiency and life. As a result, additional applications for rotary engines are being evaluated. One particularly attractive application for the rotary engine is marine use and, in particular, in outboard boat motors.
As with any other internal combustion engine where a flow of intake air is induced by operation of the engine, the intake of combustion air in a rotary engine may also be induced by engine rotation. A rotary engine may also often be air cooled or may include a combination of air and water cooling. If air cooling is utilized, cooling air flow is also induced by engine rotation. For the sake of convenience and simplicity of engine construction, a single flow of air is utilized both for engine cooling and for combustion. Thus, after a flow of air is directed through the engine rotor chamber for cooling, it is directed into the carburetor, mixed with the fuel and passed into the combustion region of the rotor chamber.
It is well known in the art of internal combustion engines, including rotary piston engines, that an induced flow of intake combustion air is not provided at a constant flow volume. Instead, the typical intake and exhaust strokes of an engine cycle (whether a two-stroke or four-stroke cycle) will result in a pulsed flow of air. The pulsed flow results in waves which travel back and forth through the intake air system such that the desirable maximum intake air volume is not always available for the intake stroke. Thus, a "tuning" or balancing of the intake air flow may be undertaken to provide a high pressure wave front pushing a maximum volume of air through the carburetor and into the combustion chamber at the most efficient point in the intake stroke.
Intake air tuning generally requires the use of an intake air conduit of substantial length but, depending upon the average engine speed at which performance is desired to be optimized, the length of the intake air conduit may vary substantially. The tuning length providing the best average performance for the specific application is, therefore, chosen with some resulting sacrifice in performance at other speeds. Unfortunately, the optimization of intake air flow at relatively low speeds in a rotary engine requires a tuned inlet air conduit of considerable length. Where a rotary engine is used in an outboard motor, the conservation of space and the need to keep overall engine size to a minimum are key considerations. Thus, the rather considerable length of an optimally tuned intake air conduit poses a significant problem in an outboard motor application.